A 48,000 year record of swiftlets (Aves: Apodidae) in North-western Borneo: Morphometric identifications and palaeoenvironmental implications

Abstract

This paper reports the results of an analysis of 508 sub-fossil carpometacarpi of swiftlets (Aves: Apodidae) recovered during archaeological excavations of the Great Cave of Niah in Sarawak, North-western Borneo. The bones date from 48kyBP (ky BP: 103 calibrated years before present [1950]) to 0.35kyBP and provide a means to consider populations of birds (of which one species is a significant commercial interest) in the context of environmental and climatic change in the past, and their responses to recent anthropogenic landscape changes in the present.Biometric analyses and comparative data indicate that the collection contained specimens attributable to the three extant species of swiftlet that currently inhabit the Great Cave: the black-nest swiftlet (Aerodramus maximus), mossy-nest swiftlet (Aerodramus salanganus) and the white-bellied swiftlet (Collocalia esculenta). A subset of 267 identified specimens provides a time series that suggests that the Great Cave and environs have sustained populations of these three species throughout last 48,000years. While changes in the wing length of extant species of swiftlet are known as a function of geographical and altitudinal range, statistical testing of a single character (greatest length of the carpometacarpus) did not indicate changes in wing length in any of the identified species.The findings indicate that the local environs maintained a sufficient abundance of aerial arthropods to support populations of these obligate insectivores and are consistent with studies that suggest that the structural diversity of forest habitats was maintained throughout the late Pleistocene (48kyBP to 11.6kyBP) and Holocene (11.6kyBP to 0.35kyBP). The findings also provide context for the recent declines of the commercially-significant black-nest swiftlet and suggest that this species may be ill-equipped to adapt to recent anthropogenic deforestation of the Niah area.